The Stock GM- ZL1 1.9 Blower is very efficient. It responds well to being overdriven. It can push a stock LSA long block very close to it's safe limit.

I was told not to overspin it cause of a few issues, heat soak being one!
And I always used 700-720whp as a pretty much max for a LSA stock internals!

But as I seen some of your work I'm not doubting you at all !! So I'm pushing 661whp now at about 13 psi! With the works done except porting the blower!

As I was wondering in the range of a 850whp monster which this blower/motor can't handle stock but the crank is super strong, rods and pistons need to be forged! But seems everyone just says " well reached stock LSA limit lets slap 427, or RHS 4**!

KB doesn't have the best reputation for building efficient blowers, the stock blower is WAAAY more efficient than the KB 2.8 unfortunately. I would have loved to use a KB because its much smaller than the 4.0, but the Whipples are superior in every possible way except packaging.

I make 705rwhp 694trq with a auto with my set-up 2013 ZL1. Love it all day long, stock block and heads.. I might do a set of heads one day and upgrade the fuel system to push 750rwhp if possible. The car runs really good right now I love it!